In current display systems employing spatial light modulators, such as liquid-crystal-display (LCD), liquid-crystal-on-silicon (LCOS), and microelectromechanical system (MEMS)-based display systems (e.g. spatial light modulators of reflective deflectable micromirrors), illumination light incident onto the spatial light modulators and thus modulated is produced by a combination of light sources producing white light, light integrators, and color filters.
Thermal light sources, such as arc lamps, are prevailingly used as the light sources to produce white light for the systems because of their high brightness with compact sizes.
The white light is conducted to the downstream optical devices, such as color filter, condensing lens, and the spatial light modulator via light integrators. A light integrator is generally a hollow internally reflective rectangular device, and uses multiple reflections of the incident light within the tunnel thereof to obtain homogenization of a generally round or non-uniform light beam by converting it into a uniform rectangular pattern. The light intensity may be reduced due to multiple reflections, but the resulting pattern is homogenized and uniform in light intensity. The reflected light is transmitted through the exit aperture as a rectangular beam, which is imaged onto the spatial light modulator. Thus, the light pipe is used to improve uniformity and preferably also match the aspect ratio of the illumination light to that of the spatial light modulator.
A color image can be generated by using more than one spatial light modulator, typically one per color (e.g. red, green and blue), and combining their images optically. Alternatively, a color display may be generated by temporarily interleaving separate images in different colors, using a color filter wheel. As the color filter wheel rotates rapidly, the color of the projected image cycles rapidly between the desired colors, typically the additive primaries red, green, and blue. When the colors are varied rapidly enough, the human eye perceives the sequential color fields as a single full-color image.
The illumination intensity and the brightness of the thermal sources, however, are proportional to the fourth power of source temperature. The high brightness and illumination intensity, therefore, are accompanied with intensive heat. Such heat propagates into and thus heats the downstream optical devices, such as the light integrator and the color filter. The heated optical devices may reach temperatures beyond their respective tolerances, resulting performance distortion, and even device failure. For example, if an arc lamp is used as the light source, intensive heat is produced accompanying the intensive illumination intensity and high brightness. Such heat propagates into the tunnel of the light integrator and may melt the adhesive typically used to bond the reflective walls of the light integrator. The intensive heat may also destroy the optical coatings on the color filter, causing device failure of the color filter.
Therefore, a method and device that efficiently dissipate produced heat from the light source and secure the thermal stability of optical devices without compromising image quality or the integrity of the system are desired.